Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!usc!pollux.usc.edu!papa
From: papa@pollux.usc.edu (Marco Papa)
Newsgroups: comp.sys.amiga
Subject: XPR External Protocols Standard (COMMERCIAL)
Message-ID: <18193@usc.edu>
Date: 1 Jul 89 03:44:54 GMT
Sender: news@usc.edu
Reply-To: papa@pollux.usc.edu (Marco Papa)
Organization: Felsina Software, Los Angeles, CA
Lines: 71

I've just sent to Bob Page, the moderator of comp.sources.amiga, the sources
for XPR, the "External File Transfer Protocols as Amiga Libraries Standard" for
allowing communication programs to 'share' protocols between each other and
provide end-users a way to write their own protocols.  XPR has been designed by
Willy Langeveld of SLAC, the author of VLT.  Since we at Felsina Software
were planning to implement a similar scheme, we decided to adopt Willy's
standard and provide input in its design.  The current design has undergone
a number of revisions and is also open to subsequent expansions if needed.
Of course VLT includes support for the XPR standard.  Felsina Software has
announced that it will include an implementation of XPR in an upcoming version
of A-Talk III.  An announcement will be made when such support will be 
available. In fact we will provide support for CIS B Plus as an XPR library 
in our first XPR-based release.  This version of course would work with VLT 
and with any other comm program, commercial, pd or shareware that decides to
support XPR.  We encourage any of these developers to join the XPR standard.
Standards are good for everybody, users as well as developers.

To give you an idea of the implementation, let me briefly quote from Willy's
Introduction from the XPR documentation:

-- beginning of quote

        XPR: External File Transfer Protocols as Amiga Libraries.
        =========================================================
                       Version - 29 June 1989
                       (C) Copyright 1989 by
                         W.G.J. Langeveld
                 Stanford Linear Accelerator Center

        One of the most frequently asked questions of the author of a
communications program is "Why don't you implement this wonderful file transfer
protocol in addition to the 25 you already have?". Clearly, implementing more
FTP's leads to larger code size and to increased product development time and
customer support requirements, unless there is a way to have the additional
protocols available as separate entities. One obvious way is to put the
additional FTP's in overlays, but that only mitigates the code size problem and
does not allow protocols to be used with communications programs of different
vendors. Better is to open the serial device as a shared port and to have a
completely separate program access it at the same time. However, this method has
the disadvantage that shared use of a single serial port can lead to
unpredictable results unless there is a well-established priority system
enforcing which program is allowed to write to the device at which time. The
advantage is that the FTP can now be developed separately and even by someone
other than the author of the communications program. There are variations
involving inter-process communication to add access control to the latter
system, but I will not go into further detail.
        The system described here is based on Amiga shared libraries. The
library implements a small number of primary functions, such as "Send File(s)"
and "Receive File(s)". These functions are called with a single argument, a
pointer to an XPR_IO structure. This structure contains a number of things, the
more obvious one being a pointer to a null terminated string indicating which
files are to be sent or received and addresses of "call-back" functions inside
the code of the communications program to access the serial device, which is
opened typically in exclusive access. The scheme described here opens the
possibility for the Amiga community to write a multitude of file transfer
protocols, all rather small in size because they don't contain any overhead,
that work with any communications program following the rules outlined in this
document.
....
        I would like to thank Marco Papa of Felsina Software for his help in
working out some of the details of the XPR standard.

---- end of quote

Have you all an enjoyable and safe forth of July.

-- Marco Papa 'Doc'
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
uucp:...!pollux!papa       BIX:papa       ARPAnet:pollux!papa@oberon.usc.edu
"There's Alpha, Beta, Gamma, Diga and Caligari!" -- Rick Unland
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=